This invention relates to a passive infrared intrusion detector of the type having a heat sensor, a lens for focusing radiation from a field of view guarded by the sensor and an alarm coupled to the sensor for providing an output when the sensor determines a change in temperature. More particularly, this invention relates to improvements in the aforesaid type of intrusion detector including the mounting and lateral aiming of the intrusion detector within the housing, a simplified window and lens mounting and removal structure, a readily removable chassis, a movable mirror which, in combination with a light source, serves to align and aim the intrusion detector, and a tamper switch and latch useful in the detection of tampering and the preliminary mounting and aiming of the device.
Passive intrusion detector systems have proven very useful in monitoring areas to detect intruders. An infrared detector is employed in such systems which detect radiation emitted by an object in the field of view such as an intruder. The system has no active source but relies on the radiation emitted by objects in the field of view of the detector. Of course, one of the problems with such a system is that it recognizes a change in temperature but cannot distinguish the source of that change in temperature. Thus, it may alarm upon change of temperature of a radiator, air vent, lamp, etc. Accordingly, the zones or areas which are to be protected by the intrusion detector must be carefully delineated and this is normally done by trial and error which is not only difficult but time consuming and expensive.
In U.S. Pat. No. 4,275,303 entitled "Passive Infrared Intrusion Detecting System", which is assigned to the assignee of the present invention, one method of dealing with this problem is disclosed. That method utilizes a lamp which emits visible light and is positioned within the intrusion detector near the sensor. Each lens segment has a distant and a near field portion. The light from the lamp passes through the lens in the direction of the zones to be protected by the detector, and the detector is adjusted until an observer can see the light from the lamp through one lens portion. The observer is then standing in a zone which is being observed by the detector through the other lens portion. Although this approach has been found to be useful, it has several shortcomings which include the fact that the detector and the lamp do not share a common field or view.
Another drawback with prior art units is that lenses (or focusing mirrors) are often integral parts of the unit. Thus it may be necessary for an installer to carry a large enough inventory to suit many different conditions of area dimensions and atmosphere. In addition, the mounting structure in which the intrusion detector is placed does not facilitate the removal of the window nor the positioning of the intrusion detector within the housing. In testing and set up it is desirable to be able to rapidly mount the housing for the intrusion detector and to be able to rapidly install or remove the intrusion detector system from its housing. This would allow the maximum flexibility in mounting and aiming the intrusion detector during installation.